The present invention relates to a structure for retaining a long optical fiber as one piece.
Generally, a long optical fiber is employed as a constituent element in an apparatus such as an optical fiber amplifier and an optical fiber gyroscope.
The optical fiber amplifier comprises, for example, an amplification optical fiber having a core thereof doped with a rare earth element such as Er. The optical amplification factor of this amplification optical fiber is the product of the concentration of the doping element and the length of the optical fiber. That is, the optical amplification factor depends on a concentration-length product.
To obtain a high amplification factor, therefore, the concentration-length product may be set large. This, however, causes disadvantages such as inhibition of turning the optical fiber amorphous if the concentration of a doping element excessively increases. For that reason, while keeping the concentration of the element in a constant range, the length of the optical fiber is increased to some extent.
In this way, if an apparatus is assembled while using a long optical fiber, it is necessary to contain the optical fiber in the apparatus as one piece.
To this end, such processings as a processing for winding a long optical fiber around a reel or that for leading and attaching the optical fiber into the apparatus, have been hitherto carried out.
If such a reel is to be used, however, dead space occurs due to the central cavity of the reel and the thickness of a collar and packaging density is disadvantageously lowered. Further, since a high strength material is used for the reel, the reel cannot be given flexibility.
In addition, if the optical fiber is led into the apparatus, it is required to fix the optical fiber to hooks or the like at predetermined pitches"" intervals while maintaining an appropriate radius of curvature so as not to increase bending loss or not to loosen the optical fiber, thereby disadvantageously taking time and labor to contain the optical fiber.
To avoid these disadvantages, there is proposed a structure in which an optical fiber is arranged in a state in which the turning positions of the optical fiber are staggered from one another planarly, and is retained by sealing it with a soft resin or the like into a sheet shape (see Japanese Patent Application No. 6-224908).
This structure has the following advantages. Since the optical fiber is formed into a sheet shape as a whole, it is thin, flexible due to use of the soft resin and is easy to package.
Nevertheless, if the optical fiber is arranged in a state in which the turning positions of the optical fiber are staggered from one another planarly, the occupied area of the optical fiber increases and the increase of the area is greater as the optical fiber becomes longer.
Furthermore, only by staggering the turning positions of the optical fiber planarly, the turning positions unavoidably intersect one another locally and large bending is generated at the intersecting parts, thereby making it impossible to sufficiently reduce loss.
It is, therefore, the first object of the present invention to allow not only integrally handling an optical fiber but also decreasing the occupied area of the optical fiber even if it is long, and stably retaining the optical fiber without causing it to get loose and without causing micro-bending or the like.
Further, if a long optical fiber integrated by a sheet-like fixing material stated above is incorporated in an apparatus, it is required to splice an externally-led optical fiber to the long optical fiber to establish connection between the apparatus with various equipment.
In that case, according to the conventional technique, the optical fiber is pulled out of the fixing material and a different type of an optical fiber is spliced to the pulled-out end portion. If so, splicing strength is weak in the splicing state, with the result that the end portion and the other optical fiber may be possibly disconnected from each other when external force, such as twist or bending, is applied to the spliced portion.
To avoid the disconnection, the conventional technique take measures such as reinforcing the spliced portion by using a splicing sleeve. If such a splicing sleeve is used, the reinforced portion becomes far thicker and far heavier than the outside diameter of the optical fiber and the reinforced portion tends to be moved. To fix it, it is necessary to take measures to separately provide a splicing sleeve holder on a substrate or the like, thereby disadvantageously taking time and labor for the assembly of the apparatus.
It is, therefore, the second object of the present invention to make a spliced portion compact and stable and allow retaining an optical fiber as well as the spliced portion integrally.
The first invention is an optical fiber retaining structure for fixedly retaining a long optical fiber as one piece, characterized in that the optical fiber is arranged to form planarly staggered turning portions without causing intersecting parts to occur, and to form a plurality of staggered turning portions laminated at a same position in a thickness direction of the optical fiber orthogonal to a plane on which the optical fiber is arranged; and the resultant optical fiber is retained integrally in a sheet-like state by a fixing material, the fixing material being a bonding agent or a film.
With this structure, it is possible to handle the long optical fiber as a piece while maintaining a thin shape thereof as a whole without causing the optical fiber to get loose, so that the optical fiber can be easily arranged in an apparatus. Besides, since the optical fiber does not have an intersecting part at the intermediate portion of the fiber, there is no fear of the occurrence of bending loss. Further, such a plural layer winding structure, in particular, can greatly reduce an occupied area of the optical fiber and, therefore, improve packaging density.
The second invention is based on the first invention and characterized in that an externally-led optical fiber is spliced with each end portion of the optical fiber, and that a spliced portion is contained within the fixing material. Due to this, the entire retaining structure including the spliced portion can be made compact, thereby facilitating connection with various equipment.
The third invention is an optical fiber retaining structure for fixedly retaining a long optical fiber as one piece, characterized in that the optical fiber is arranged to planarly form staggered turning portions without causing intersecting parts to occur without overlapping with one another at a same position, and the resultant optical fiber is retained in a sheet-like state integrally by a fixing material, the fixing material being a bonding agent or a film; and an externally-led optical fiber is spliced to each end portion of the optical fiber and a spliced portion is contained within the fixing material. Therefore, even with a one-layer winding structure, the entire retaining structure including the spliced portion can be made compact, thereby facilitating connection with various equipment.
The fourth invention is based on any one of the first to third inventions and characterized in that the optical fiber has an S-shaped innermost side serving as a winding start portion and sequentially wound in a track shape from the winding start portion toward a winding end portion. Therefore, the portion on which the optical fiber is led from the fixing material becomes linear, which linear shape is advantageous in connection with another optical fiber. Besides, with this structure, a twist does not occur and the long optical fiber can be contained in a compact manner in an apparatus.
The fifth invention is an optical fiber retaining structure characterized in that a plurality of the optical fiber retaining structure according to the first to fourth inventions are combined in an optical fiber continuous state and the combined retaining structures are superposed in a thickness direction of a fixing material to thereby form another optical fiber retaining structure; and turning directions of superposed, adjacent upper and lower retaining structures are set to face opposite to each other. Therefore, a twist does not occur to a portion on which a continuous optical fiber moves from one of the upper and lower retaining structures to the other, whereby the increase of loss and the like can be avoided.
The sixth invention is based on any one of the first to fifth inventions and characterized in that a fixing member such as a washer is integrally retained by the fixing material at a different position from a position of the optical fiber. It is, therefore, possible to obtain a retaining structure having an attachment portion for attaching the structure to various equipment in advance, facilitating attaching the structure to the equipment.
The seventh invention is based on any one of the second to sixth inventions and characterized in that the spliced portion is subjected to a re-coating processing. As a result, the spliced portion is covered with the fixing material after being subjected to a re-coating processing, thereby ensuring the protection of the spliced portion.
The eighth invention is based on any one of the first to seventh inventions and characterized in that a spliced position, at which the optical fibers are spliced with each other, of the spliced portion is fitted into a protection holder, the protection holder sealed by the fixing member. This can further ensure the protection of the spliced portion compared with the seventh invention.
The ninth invention is based on any one of the first to eighth inventions and characterized in that a perforated notch is formed in an optical fiber leading-side end portion of the fixing material. The tenth invention is based on any one of the first to eighth inventions and characterized in that a concave portion is formed on an optical fiber leading-side end portion of the fixing material in an optical fiber leading direction. Further, the eleventh invention is based on any one of the first to eighth inventions and characterized in that a notch is formed in a part of an outer peripheral portion of the fixing material to thereby provide a flexible piece at the fixing material; and an optical fiber leading-side end portion is positioned at the flexible piece. As can be seen, according to the ninth to eleventh inventions, the fixing material is easily bent in the thickness direction thereof, so that it is possible to prevent the bending or the like of the optical fiber.
The twelfth invention is based on any one of the first to eleventh inventions and characterized in that the fixing material is formed by connecting two films to each other with the optical fiber vertically put between the two films. This laminated structure facilitates fixedly sealing the optical fiber.
The thirteenth invention is based on the twelfth invention and characterized in that a bonding agent is coated on at least one of surfaces of the films, the surfaces facing each other. This can further facilitate operation for fixedly sealing the optical fiber to the fixing material.
The fourteenth invention is based on any one of the first to eleventh inventions and characterized in that the fixing material is made of a mold material for sealing the optical fiber. If the optical fiber is sealed by a mold material, the optical fiber can be retained more rigidly, making it difficult to exert the influence of external pressure on the structure.
The fifteenth invention is based on any one of the first to fourteenth inventions and characterized in that an input and output connector is provided at each end portion of the optical fiber. This facilitates connecting the optical fiber with the optical fiber of another equipment compared with a case where the optical fibers are spliced with each other.
The sixteenth invention is a light amplifier characterized in that the light amplifier has an optical fiber retaining structure according to any one of the first to fifteenth inventions; and the optical fiber consists of an amplification optical fiber having a core doped with an rare earth element. This can facilitate assembly of an apparatus and make the overall apparatus small in size.